1. Field of the Invention
The invention relates to the field of surface treatments of substrates, whether these are metallic or non-metallic, such as, polymer, textile, paper, glass, or even wood, plaster or tile substrates, and whether these substrates are flat or are in the form of a volume, these substrates being used in extremely varied fields including metallurgy, bottle-making, flat glass, plastic packaging, etc.
2. Description of the Related Art
It is known that these surface treatments are usually carried out for the purpose of improving the adherability and wettability of these substrates, or else for introducing a friction coefficient, corrosion resistance, color, an optical index, etc.
Among the very numerous methods available in the literature for carrying out these surface treatments are liquid-phase treatments, low-pressure plasma treatments, corona-discharge treatments or flame brushing.
The Applicant has recently proposed, in documents EP-A-734 461 and EP-A-734 462, a process for depositing silicon-based layers on a substrate, in which process the substrate is placed in the remote-plasma position of an apparatus for forming excited or unstable gaseous species so as to be brought into contact with a gaseous treatment atmosphere necessary for producing the coating, obtained from the following two components:
a primary gas treatment mixture, as obtained at the gas outlet of the apparatus, which comprises excited or unstable gaseous species resulting from the transformation in the apparatus of an initial gas mixture; and
an adjacent gas treatment mixture which comprises a gaseous silicon precursor and which has not passed through the apparatus in question.
These European documents, together with document FR-A-2 692 730 also in the name of the Applicant, disclose a device for forming excited or unstable gaseous species, operating approximately at atmospheric pressure, and suitable for implementing the process described in the abovementioned European documents.
Although these processes undoubtedly constitute an advance over the existing techniques (liquid phase, flame brushing, low-pressure plasma, etc.), the Applicant has shown by its studies that there may be further improved, especially so as to increase the transformation efficiency of the reactive gas (for example silane) and to reduce the production of undesirable particles (powders).
Specifically, an insufficient transformation efficiency of the reactive gases correspondingly limits the rate of growth of the layer deposited and therefore the productivity and economic benefit of the process.
It is one of the objectives of the present invention to provide a solution to the abovementioned technical problems.
To do this, the invention relates to a process for forming a coating on a substrate, in which the following steps are carried out:
at least one apparatus for forming excited or unstable gaseous species is used, in which an initial gas treatment mixture is transformed so as to obtain, at the gas outlet of the apparatus, a primary gas treatment mixture which comprises excited or unstable gaseous species and which is substantially free of electrically charged species;
the substrate is brought into contact, at a pressure close to atmospheric pressure, with a gaseous treatment atmosphere in order to deposit the coating, this atmosphere being obtained from the primary gas mixture and an adjacent gas treatment mixture which comprises at least one gaseous precursor needed to form the desired coating, and which has not passed through the said apparatus;
the process being characterized in that the adjacent gas mixture is injected into the stream of primary gas mixture as obtained at the gas outlet of the apparatus.
The process according to the invention may moreover have one or more of the following technical characteristics:
the injection of the adjacent gas mixture into the stream of primary gas mixture is made in the following manner:
i) means are used for separating the stream of primary gas treatment mixture, as obtained at the gas outlet of the apparatus, into at least two separate streams;
j) the injection of adjacent gas mixture is made to enter between said at least two separate streams of primary mixture;
the residual oxygen content of the gaseous treatment atmosphere is less than 500 ppm and preferably between 5 and 100 ppm;
the dew point of the gaseous treatment atmosphere is less than xe2x88x9220xc2x0 C. and preferably less than xe2x88x9230xc2x0 C.;
throughout or during part of the time the substrate is in contact with the gaseous treatment atmosphere, the substrate is at a temperature of between 50 and 350xc2x0 C., and more preferably between 100 and 300xc2x0 C. (whether the substrate undergoes heating during the contact or else, for example, whether it reaches the contact zone already hot);
the treated substrate is brought opposite the gas outlet of said apparatus, where appropriate opposite the gas outlets of several apparatuses placed in parallel over the width of the substrate and/or successively opposite the gas outlets of several apparatuses placed in series, by a conveying system passing through an internal space bounded by a shrouding assembly isolated from the surrounding atmosphere, the assembly being connected in a sealed manner to the apparatus or including the apparatus;
the nature of the coating produced on the substrates belongs to one of the following categories: a metal oxide or a metal oxynitride;
the coating produced is a coating comprising silicon and the adjacent gas treatment mixture therefore includes at least one gaseous silicon precursor;
at least one of said apparatuses, in which the initial gas treatment mixture is transformed, is the site of an electrical discharge created between a first electrode and a second electrode which extend in an elongated main direction, the initial gas mixture passing through the discharge transversely to the electrodes and to this main direction; and
a layer of a dielectric material is placed on the surface of at least one of the electrodes, opposite the other electrode.
The invention also relates to an installation for forming a coating on a substrate, suitable especially for implementing the process described above, and comprising:
at least one apparatus for forming excited or unstable gaseous species, which is capable of transforming an initial gas treatment mixture so as to obtain, at the gas outlet of the apparatus, a primary gas treatment mixture which comprises excited or unstable gaseous species and which is substantially free of electrically charged species;
means for feeding an adjacent gas treatment mixture, comprising at least one gaseous precursor needed to form the coating, which does not pass through the apparatus, and is capable of forming, with the primary gas treatment mixture as obtained at the gas outlet of the apparatus, a gaseous treatment atmosphere to be brought into contact, at a pressure close to atmospheric pressure, with the substrate in order to produce the coating;
the installation being characterized in that said means for feeding the adjacent gas mixture allow it to be injected into the stream of primary gas mixture as obtained at the gas outlet of the apparatus.
According to one of the embodiments of the installation according to the invention, the means for feeding the adjacent gas mixture into the stream of primary gas mixture comprise:
i) means for separating the stream of primary gas mixture as obtained at the gas outlet of the apparatus into at least two separate gas streams;
j) means for injecting the adjacent gas mixture between said at least two separate streams of primary gas mixture.